off I believe that I must tell the reader a bit about myself and how I
came to learn what I am about to place on paper. In 1980, I applied for a
got a Federal Firearms License as a way to support my love and hobby of
firearms. This allowed me to legally buy and sell firearms across the
state line and to ship and receive firearms across the state line.
my love and license turned into a nearly full-time business of selling
and repairing firearms out of my home. This also led me to get involved
with another gentleman, also a FFL holder, and a business venture of
applying a Teflon based coating on firearms as a weatherproof
alternative to bluing. This venture grew over the course of five years
to the point that it was no longer fun. It took my entire life and my
wife's also, so we decided that it was time to stop. The time that I had
available led me back into LBC's and to the sharing of my experiences
someone speaks of media blasting he can be talking about several medias.
Below is a partial list along with a bit of info about each.
Commonly know as sandblasting. Sand, or silica sand, comes in several
grits sizes and is the most common of the medias. It is available nearly
everywhere from building supply stores and hardware stores to specialty
dealers. It is cheap and easily handled in 50# or 100# bags.
It is used
only once and is discarded after use. In times past used sandblasting
sand often was just left on the ground at the site that it was used.
OSHA and EPA have gotten involved and declared that used sandblast sand
is a hazardous chemical because of the bits of paint and metal that is
with it and must be disposed of in a fitting manner. Sand is also rather
soft as blast media goes so it breaks up readily. When it breaks up it
forms silica dust that can be inhaled. This can lead to a very serious
disease called 'silicosis'. Silicosis is similar to black lung in the fact
that the dust gets into the lungs and stays there forever thus reducing
you ability to breath. Sand can be used in an enclosed cabinet however
the fact that it breaks up so readily makes seeing hard and quickly
reduces your blasting ability as particles get smaller. As a general
rule stay away from sand in an enclosed cabinet and outside if you can.
Slag has become a cheap alternative to sand. The slag is created as a
waste product in the production of iron. It is like glass powder.
available under a variety of names, one of which is A Black Beauty.
tried this stuff when my supplier gave me a couple of free bags to try.
When I was working on guns I was blasting a lot of small parts, some of
which were case hardened. I found that this media would work OK for some
of my jobs but would not even touch the hardened steel parts. I was
searching for a media that would provide an uniform surface finish on
all the materials used in construction of firearms. This was not it!
Slag was available in several grits, and was cheap, less that $2 a bag.
The down side was that it broke up in use much like sand so it required
keeping several hundred pounds on hand at all times and then dumping the
old used grit and replacing, both of which required more time than I
had. In addition to the fact that it was not hard enough to provide the
finish that I required it was not worth my time to mess with. It would
work fine in an outside blasting situation where you did not reuse the
grit, and like sand, many people use it for this. It too, becomes
hazardous waste upon use.
Oxide: Aluminum Oxide
(Alox) was my savior. Alox is used in making abrasive
paper and cloth so you know that it is hard enough to cut metal. Alox
was hard enough to affect the hardened steel gun parts. It also was hard
enough that it did not break up in use like the other medias did. The
problem here is that it is not cheap! So far I have been talking about
media that cost less than 2 bucks a bag. Alox was costing me closer to
$20 for a 50# bag. That was the down side. The up side is that it made
little dust, and seemed to last forever. It was not as readily available
as the others but I had a good supplier that would always keep a couple
hundred pounds in stock for me but I had to drive 75 miles to get it.
Shipping via UPS was expensive. This is the media that I settled on for
most of my work. It comes in several grits. I used 60#, which gave a
rather coarse finish that was begging for paint.
Silicone carbide is an even harder media than Alox. It will
attack almost anything. It is also at least twice the cost and a lot
harder to find. I had a small amount as a sample but decided that the
benefits did not out weigh the extra cost, so I never did any serous
testing with it.
Glass beads are available in a multitude of grades. Glass has a
couple of disadvantages. One is the fact that it is not hard enough to
attack all materials. Another is the fact that the beads are rather
fragile and should be used with less than 80# air pressure to keep them
from breaking up prematurely. The beads are perfectly round, and being
perfectly round they leave round indentions in the metal that they are
used on. This make a neat finish because of the way that light is
reflected off the surface. Coarse beads will create a sort of pearl
finish that appears to be a foot thick. The finer the grit, the smaller
the spherical indentions, the less of this effect you have. Also, the
fact that you have rounded indentions gives paint a less desirable
surface to bind to as compared to the other medias mentioned above.
my shop now I maintain one cabinet with coarse glass beads for my
general purpose blaster. When I rebuild an engine all the internal parts
are blasted in this cabinet. It made the rods and rockers come out
BEAUTIFUL! Glass beads are also available in combination with Alox for a
more general purpose media. One drawback with beads is the fact the will
break up rapidly if you use too much pressure. I try to maintain around
60# in my glass bead cabinet.
There are other medias that I have no experience with. Just to make
you aware of their availability I will list them.
or aluminum shot
of these have their applications. Some would be cleaning paint off of
metal without affecting the metal. Another would be removing rust
without affecting the blast metal. Naturally, the softer the base metal
the softer the grit need to be.
blasting equipment can be broken up into two main systems and then
subsystems under those.
Blasting: This is the familiar pressure pot that you see in use
sandblasting large equipment like tanks and bridges and such. This is
mostly used outside in the open but there are a couple of setups that I
have seen that used a self enclosed and circulating box with a
pressure blaster. I have also seen self enclosed rooms where a operator
gets inside and walks around while blasting a object while the grit used
falls though the floor to be reused over and over. Neat, but it does not
have anything to do with this discussion except for the fact that it
would be neat to use a setup like this on a LBC!
This is the system that you are most likely to run across and
use in our hobby. There are pots for use with a siphon blasting gun for
exterior use but they are SLOW to try to do a whole car with. Most
cabinets are of the siphon variety. Both of my setup are of this type.
are available in nearly any size from shoebox size to ones big enough to
put an entire fender in. When it come to size you cannot have a cabinet
that is too big as there is always something larger than your cabinet
that you need to blast! Cabinets can be homemade, as my first one was,
or factory made. In hindsight, I would never attempt to make another one
myself because there are too many nice cabinets available to justify
spending your time trying to design something that you will be unhappy
with later. That said, I will tell you what makes a good cabinet, in my
First, a cabinet has to be air tight.
You will need to run you
cabinet under a slight vacuum in order to control the dust created
within. If you disregard this you will have one big mess on your hands.
Think about it - you will be adding air to a box at a rate of 10-15 scfm.
That air has to go somewhere after it get there. If you have not
provided for this air and dust will emerge from ever crack that you knew
about and a bunch that you didn't. Believe me, I've been there!
your box will have to have a funnel shaped bottom to be able to feed
your blaster. Just a little slope won't do. Sides need to be at least 45
degrees. The only time that grit will flow like water is when you have a
hole and you are trying to keep the grit inside-then it will go all over
the floor. Your funnel needs to have an opening in the bottom so that
you can drain the grit out when you want to change it out. This opening
also needs to be high enough above the ground so that you can get a pail
or box under it to catch the grit.
Third, you need a window to be able
to see what you are doing through. This window needs to be covered with
a layer of plastic to protect the glass from the grit. My first box used
just a layer of window glass and in a short period of time it was
ruined. I started cutting up 3-liter coke bottle and using this to cover
the glass. This worked OK but I could not drink enough cokes to keep up!
Fourth, you need a source of light to see by. Some of the commercial
boxes have a flood lamp mounted inside. This sucks because the grit gets
up in the socket and destroys everything after a short period of time.
In addition to this there is always the likelihood of hitting the bulb
and breaking it at the most inopportune time - been there, done that.
now use a florescent trouble light mounted on the outside of my window.
It is out of the way and protected from the grit. The ideal solution
would be to have another window on the top of your box with a light
behind it. Next, you need access to the inside with your hands.
I took a
pair of rubber gloves and had my wife sew them to a pair of jean
legs. It worked for a while but you will learn that the left glove
always wears out first if you are right handed. You unknowingly blast
the dickens out of the thumb and forefinger while you are holding your
target. Naturally all this needs to be at a comfortable work height.
spent eight hours a day in front of my cabinets. More than five minutes
of bending over will give me a backache big time!
Next, you have to have
some method of dust collection. I can hear what you are thinking -
shop vac will not do! I went through three of them before I learned.
Most shop vac's use the air that you are sucking to pass through the
motor and cool things off. OK, think what is going to happen when you
put a bunch of Alox in this air. Goodbye brushes, goodbye bearings!
I know, the shop vac has a filter, but it ain't enough of a filter, and
it only takes one small hole to let enough grit through to destroy a
motor! Buy a Dust collector that is made for the job and save yourself
money in the long run or work out a deal to buy vac cleaner motors by
the case from WW Grainger! Been there, done that!
last and most important item I saved for last - the gun/nozzle. I will
call it the head from here on out 'cuz head is easier to type and my
fingers are getting tired. There are good one available and there are
cheap ones. I have had both. I will never buy another cheap one!
head has to stand up to the flow of both the air and the grit. It is
basically an aspirator-air flowing through a venturi tube create a
vacuum to suck the grit up from the bottom of the box. The cheap one are
made of some pot metal alloy. The good ones look the same but they have
a steel liner in the proper place to keep the grit from eating it up.
They both look the same on the outside. There is a company called TIP
that specializes in blasting equipment. They sell everything that you
will need. Go to their website, http://www.tptools.com, and order a
catalog. You may not thank me if you do it now but if you mess around
trying to cut corners and do it later you will say why didn't I do this
sooner. Their catalog is worth it even if you had to pay for it, which
you don't. Nozzles are available in three materials. First is mild
steel. This is the cheapest and it reflects in the life if the nozzle.
Grit will eat it up in a hurry. If you are not careful it will destroy
your head at the same time. Next is ceramic. Ceramic is harder and
tougher than mild steel but is brittle. Cost is naturally higher than
steel. Last, we have the Cadillac, 'er excuse, the Rolls of the nozzles.
It is made of tungsten. This is the one you want if you are going to do
much blasting. It will last and last and last. It is however, expensive.
use nothing but tungsten!
if this has not been confusing enough already I am going to throw some
more at you. Nozzles come in three sizes. The size needed depends on
the air flow that you have available. They are- 13/64", small,
requires 4-8 scfm, 1/4", medium, requiring 10-15 scfm, and
5/16", large requiring 20-25scfm. This is where thing get critical.
If you do not have enough air flow you will not suck the grit up and
through the head. Too much air is not a problem but you are not using
all of you capabilities. In both of my cabinets I use medium nozzles.
have two Campbell Hausfeld 5hp, two stage compressors with 80 gallon
tanks. Each compressor will put out about 12 scfm at 125#. This is
barely enough to get by running two cabinets. In choosing a compressor
you need to know how much air you will need. Ideally, your compressor
should put out 30-50% more flow at your required pressure than you need.
This will allow you compressor to cycle off in times of heavy use.
you use more air that your compressor can provide your pressure will
slowly drop to the point where you blasting will suffer. The tank size
will act as a buffer of sorts to lengthen your blasting time but is no
substitute for enough compressor. One thing that a larger tank will do
is to help cool your air a bit to allow moisture to condense out while
in the tank. Blasting cannot tolerate ANY moisture without plugging
things up. If you must have a compressor with a small tank you can rig
up a coil of 2" copper tubing in a five gallon bucket of water and
then a water separator downstream to help. You will also need a
regulator/separator at the point of use to get the last bit of water
out. Down here in south LA where humidity runs 100% most of the time I
have to go to extremes to deal with moisture. One more thing, put your
compressor outside, on a concrete pad under a roof, blow the tank down
and check the oil level every day.